package com.xiaoyi.common.security;

import org.apache.commons.lang3.StringUtils;

import java.io.UnsupportedEncodingException;
import java.util.HashMap;
import java.util.Map;

/**
 * Base64编码
 */
public final class B64Encrypter {
    static final String DEFAULT_ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    private static Map<String, B64Encrypter> coderMap = new HashMap<String, B64Encrypter>();
    private static char[] defaultEncodeChars = new char[]{
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
            'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
            'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
            'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
            'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
            'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7',
            '8', '9', '+', '/'
    };
    private static byte[] defaultDecodeChars = new byte[]{
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, 62, -1, -1, -1, 63, 52, 53,
            54, 55, 56, 57, 58, 59, 60, 61, -1, -1,
            -1, -1, -1, -1, -1, 0, 1, 2, 3, 4,
            5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
            25, -1, -1, -1, -1, -1, -1, 26, 27, 28,
            29, 30, 31, 32, 33, 34, 35, 36, 37, 38,
            39, 40, 41, 42, 43, 44, 45, 46, 47, 48,
            49, 50, 51, -1, -1, -1, -1, -1
    };

    static {
        coderMap.put(DEFAULT_ALPHABET, new B64Encrypter(defaultEncodeChars, defaultDecodeChars));
    }

    private char[] base64EncodeChars;
    private byte[] base64DecodeChars;

    private B64Encrypter(char[] base64EncodeChars, byte[] base64DecodeChars) {
        this.base64EncodeChars = base64EncodeChars;
        this.base64DecodeChars = base64DecodeChars;
    }

    public String encode(byte[] data) {
        StringBuffer sb = new StringBuffer();
        int len = data.length;
        int i = 0;
        int b1, b2, b3;
        while (i < len) {
            b1 = data[i++] & 0xff;
            if (i == len) {
                sb.append(base64EncodeChars[b1 >>> 2]);
                sb.append(base64EncodeChars[(b1 & 0x3) << 4]);
                sb.append("**");
                break;
            }
            b2 = data[i++] & 0xff;
            if (i == len) {
                sb.append(base64EncodeChars[b1 >>> 2]);
                sb.append(base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
                sb.append(base64EncodeChars[(b2 & 0x0f) << 2]);
                sb.append("*");
                break;
            }
            b3 = data[i++] & 0xff;
            sb.append(base64EncodeChars[b1 >>> 2]);
            sb.append(base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
            sb.append(base64EncodeChars[((b2 & 0x0f) << 2) | ((b3 & 0xc0) >>> 6)]);
            sb.append(base64EncodeChars[b3 & 0x3f]);
        }
        return sb.toString();
    }

    public byte[] decode(String str) throws UnsupportedEncodingException {
        StringBuffer sb = new StringBuffer();
        byte[] data = str.getBytes(Charset.ASCII.VALUE);
        int len = data.length;
        int i = 0;
        int b1, b2, b3, b4;
        while (i < len) {
            /* b1 */
            do {
                b1 = base64DecodeChars[data[i++]];
            } while (i < len && b1 == -1);
            if (b1 == -1)
                break;
            /* b2 */
            do {
                b2 = base64DecodeChars[data[i++]];
            } while (i < len && b2 == -1);
            if (b2 == -1)
                break;
            sb.append((char) ((b1 << 2) | ((b2 & 0x30) >>> 4)));
            /* b3 */
            do {
                b3 = data[i++];
                if (b3 == 61)
                    return sb.toString().getBytes(Charset.ISO8859_1.VALUE);
                b3 = base64DecodeChars[b3];
            } while (i < len && b3 == -1);
            if (b3 == -1)
                break;
            sb.append((char) (((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));
            /* b4 */
            do {
                b4 = data[i++];
                if (b4 == 61)
                    return sb.toString().getBytes(Charset.ISO8859_1.VALUE);
                b4 = base64DecodeChars[b4];
            } while (i < len && b4 == -1);
            if (b4 == -1)
                break;
            sb.append((char) (((b3 & 0x03) << 6) | b4));
        }
        return sb.toString().getBytes(Charset.ISO8859_1.VALUE);
    }

    public static boolean checkAlphabet(String alphabet) {
        if (StringUtils.isBlank(alphabet) || alphabet.length() != 64) return false;
        byte[] temp = new byte[128];
        for (int i = 0; i < 64; i++) {
            if (temp[alphabet.charAt(i)] > 0) {
                return false;
            }
            temp[alphabet.charAt(i)] = 1;
        }
        return true;
    }

    public static B64Encrypter getInstance() {
        return getInstance(DEFAULT_ALPHABET);
    }

    public static B64Encrypter getInstance(String alphabet) {
        if (!checkAlphabet(alphabet)) return null;

        B64Encrypter coder = coderMap.get(alphabet);
        if (coder == null) {
            char[] encodeChar = new char[64];
            byte[] decodeChar = new byte[128];
            for (int i = 0; i < 64; i++) {
                encodeChar[i] = alphabet.charAt(i);
                decodeChar[encodeChar[i]] = Integer.valueOf(i).byteValue();
            }
            coder = new B64Encrypter(encodeChar, decodeChar);
            coderMap.put(alphabet, coder);
        }
        return coder;
    }

    public static String encrypt(byte[] plainText) {
        return plainText == null ? null : getInstance().encode(plainText);
    }

    public static byte[] decrypt(String ciphertext) throws UnsupportedEncodingException {
        return StringUtils.isBlank(ciphertext) ? null : getInstance().decode(ciphertext);
    }
}
